Earth Science, 12eEarth Science, 12e

The Atmosphere: The Atmosphere: Composition, Structure, Composition, Structure,

and Temperatureand TemperatureChapter 16Chapter 16

Figure 16.1AFigure 16.1A

Figure 16.1BFigure 16.1B

Figure 16.1CFigure 16.1C

Weather and climate Weather and climate

Weather Weather • Weather is over a short period of time Weather is over a short period of time • Constantly changingConstantly changing

ClimateClimate• Climate is over a long period of time Climate is over a long period of time • Generalized composite of weather Generalized composite of weather

Figure 16.3Figure 16.3

Weather and climateWeather and climate

Elements of weather and climate Elements of weather and climate • Properties that are measured regularly Properties that are measured regularly • Most important elementsMost important elements

• TemperatureTemperature• HumidityHumidity• CloudinessCloudiness• PrecipitationPrecipitation• Air PressureAir Pressure• Wind speed and directionWind speed and direction

Composition of the Composition of the atmosphereatmosphere

Air is a mixture of discrete gasesAir is a mixture of discrete gases Major components of clean, dry air Major components of clean, dry air

• Nitrogen (NNitrogen (N22) – 78%) – 78%

• Oxygen (OOxygen (O22) – 21%) – 21%

• Argon and other gases Argon and other gases • Carbon dioxide (COCarbon dioxide (CO22) – 0.038% – absorbs ) – 0.038% – absorbs

heat energy from Earth heat energy from Earth

Proportional volume of Proportional volume of gases that compose dry airgases that compose dry air

Figure 16.4

Composition of the Composition of the atmosphereatmosphere

Variable components of air Variable components of air • Water vapor Water vapor

• Up to about 4% of the air’s volumeUp to about 4% of the air’s volume• Forms clouds and precipitationForms clouds and precipitation• Absorbs heat energy from Earth Absorbs heat energy from Earth

• AerosolsAerosols• Tiny solid and liquid particles Tiny solid and liquid particles • Water vapor can condense on solidsWater vapor can condense on solids• Reflect sunlightReflect sunlight• Help color sunrise and sunset Help color sunrise and sunset

Figure 16.5AFigure 16.5A

Figure 16.5BFigure 16.5B

Figure 16.2Figure 16.2

Figure 16.AFigure 16.A

Structure of the atmosphere Structure of the atmosphere

Pressure changes Pressure changes • Pressure is the weight of the air above Pressure is the weight of the air above • AverageAverage sea level pressuresea level pressure

• Slightly more than 1,000 millibarsSlightly more than 1,000 millibars• About 14.7 pounds per square inch About 14.7 pounds per square inch

• Pressure decreases with altitude Pressure decreases with altitude • One-half of the atmosphere is below 3.5 miles One-half of the atmosphere is below 3.5 miles

(5.6 km) (5.6 km) • Ninety percent of the atmosphere is below 10 Ninety percent of the atmosphere is below 10

miles (16 km) miles (16 km)

Figure 16.6

Atmospheric pressure variation

with altitude

Structure of the atmosphere Structure of the atmosphere Atmospheric layers based on Atmospheric layers based on

temperature temperature • TroposphereTroposphere

• Bottom layerBottom layer• Temperature decreases with altitude – called Temperature decreases with altitude – called

the the environmental lapse rateenvironmental lapse rate • 6.5˚C per kilometer (average)6.5˚C per kilometer (average)• 3.5˚F per 1,000 feet (average)3.5˚F per 1,000 feet (average)

• Thickness varies – average height is 12 kmThickness varies – average height is 12 km• Outer boundary is named the Outer boundary is named the tropopausetropopause

Structure of the atmosphere Structure of the atmosphere Atmospheric layers based on Atmospheric layers based on

temperature temperature • StratosphereStratosphere

• About 12 km to 50 km About 12 km to 50 km • Temperature increases at topTemperature increases at top

• Outer boundary is named the Outer boundary is named the stratopausestratopause • MesosphereMesosphere

• About 50 km to 80 kmAbout 50 km to 80 km• Temperature decreasesTemperature decreases• Outer boundary is named the Outer boundary is named the mesopause mesopause

Structure of the atmosphere Structure of the atmosphere

Atmospheric layers based on Atmospheric layers based on temperature temperature • ThermosphereThermosphere

• No well-defined upper limitNo well-defined upper limit• Fraction of atmosphere’s mass Fraction of atmosphere’s mass

• Gases moving at high speeds Gases moving at high speeds

Thermal structure of Thermal structure of the atmospherethe atmosphere

Figure 16.8

Earth–Sun relations Earth–Sun relations

Earth motions Earth motions • RotatesRotates on its axison its axis• RevolvesRevolves around the Sunaround the Sun

SeasonsSeasons• Result ofResult of

• Changing Sun angle Changing Sun angle • Changing length of daylight Changing length of daylight

Relationship of Sun angle to Relationship of Sun angle to the path of solar radiation the path of solar radiation

Figure 16.12

Relationship of Sun angle Relationship of Sun angle and solar radiation received and solar radiation received

Figure 16.11

EarthEarth––Sun relationshipsSun relationships

Figure 16.13

Daily paths of the Sun at Daily paths of the Sun at 4040º N latitudeº N latitude

Figure 16.10 A

Figure 16.10BFigure 16.10B

Figure 16.10CFigure 16.10C

Earth–Sun relations Earth–Sun relations SeasonsSeasons

• Caused by Earth’s changing orientation to Caused by Earth’s changing orientation to the Sunthe Sun• Axis is inclined 23½º Axis is inclined 23½º • Axis is always pointed in the same direction Axis is always pointed in the same direction

• Special days (Northern Hemisphere) Special days (Northern Hemisphere) • Summer solstice Summer solstice

• June 21–22 June 21–22 • Sun’s vertical rays are located at the Sun’s vertical rays are located at the Tropic Tropic

of Cancerof Cancer (23½º N latitude) (23½º N latitude)

Earth–Sun relations Earth–Sun relations SeasonsSeasons

• Special days (Northern Hemisphere) Special days (Northern Hemisphere) • Winter solsticeWinter solstice

• December 21–22 December 21–22 • Sun’s vertical rays are located at the Sun’s vertical rays are located at the Tropic Tropic

of Capricornof Capricorn (23½º S latitude) (23½º S latitude)• Autumnal equinox Autumnal equinox

• September 22–23September 22–23• Sun’s vertical rays are located at the Sun’s vertical rays are located at the

EquatorEquator (0º latitude) (0º latitude)

Earth–Sun relations Earth–Sun relations

SeasonsSeasons• Special days (Northern Hemisphere) Special days (Northern Hemisphere)

• Spring (Vernal) equinoxSpring (Vernal) equinox • March 21–22March 21–22• Sun’s vertical rays are located at the Sun’s vertical rays are located at the

EquatorEquator (0º latitude) (0º latitude)

Characteristics of the Characteristics of the solstices and equinoxessolstices and equinoxes

Figure 16.14

Table 16.1Table 16.1

Figure 16.16Figure 16.16

Atmospheric heating Atmospheric heating Heat is always transferred from warmer Heat is always transferred from warmer

to cooler objects to cooler objects Mechanisms of heat transfer Mechanisms of heat transfer

• ConductionConduction through molecular activity through molecular activity • ConvectionConvection

• Mass movement within a substance Mass movement within a substance • Usually vertical motions Usually vertical motions

• RadiationRadiation (electromagnetic radiation) (electromagnetic radiation) • Velocity: 300,000 kilometers (186,000 miles) Velocity: 300,000 kilometers (186,000 miles)

per second in a vacuum per second in a vacuum

Mechanisms of heat transferMechanisms of heat transfer

Figure 16.17

Atmospheric heating Atmospheric heating Mechanisms of heat transfer Mechanisms of heat transfer

• Radiation Radiation (electromagnetic radiation) (electromagnetic radiation) • Consists of different wavelengths Consists of different wavelengths

• Gamma (very short waves)Gamma (very short waves)• X-rays X-rays • Ultraviolet (UV) Ultraviolet (UV) • VisibleVisible• InfraredInfrared• Microwaves and radio wavesMicrowaves and radio waves

The electromagnetic The electromagnetic spectrumspectrum

Figure 16.18

Figure 16.19Figure 16.19

Atmospheric heating Atmospheric heating Mechanisms of heat transfer Mechanisms of heat transfer

• Radiation Radiation (electromagnetic radiation) (electromagnetic radiation) • Governed by basic laws Governed by basic laws

• All objects, at whatever temperature, emit All objects, at whatever temperature, emit radiation radiation

• Hotter objects radiate more total energy per Hotter objects radiate more total energy per unit area than do cooler objects unit area than do cooler objects

• The hotter the radiating body, the shorter The hotter the radiating body, the shorter the wavelength of maximum radiationthe wavelength of maximum radiation

• Objects that are good absorbers of radiation Objects that are good absorbers of radiation are good emitters as well are good emitters as well

Atmospheric heating Atmospheric heating Incoming solar radiation Incoming solar radiation

• Atmosphere is largely transparent to Atmosphere is largely transparent to incoming solar radiation incoming solar radiation

• Atmospheric effectsAtmospheric effects• Reflection – albedoReflection – albedo (percent reflected) (percent reflected)• ScatteringScattering• Absorption Absorption

• Most visible radiation reaches the surface Most visible radiation reaches the surface • About 50% absorbed at Earth’s surface About 50% absorbed at Earth’s surface

AlbedoAlbedo

Figure 16.22

Average distribution of Average distribution of incoming solar radiationincoming solar radiation

Figure 16.20

Figure 16.FFigure 16.F

Atmospheric heating Atmospheric heating Radiation from Earth’s surface Radiation from Earth’s surface

• Earth reradiates radiation (terrestrial Earth reradiates radiation (terrestrial radiation) at the longer wavelengths radiation) at the longer wavelengths

• Longer wavelength terrestrial radiation is Longer wavelength terrestrial radiation is absorbed by absorbed by • Carbon dioxide and Carbon dioxide and • Water vapor in the atmosphere Water vapor in the atmosphere • Lower atmosphere heated from Earth’s surface Lower atmosphere heated from Earth’s surface

• Heating of the atmosphere is termed the Heating of the atmosphere is termed the greenhouse effectgreenhouse effect

The heating of The heating of the atmospherethe atmosphere

Temperature measurement Temperature measurement

Daily maximum and minimumDaily maximum and minimum Other measurementsOther measurements

• Daily mean temperature Daily mean temperature • Daily rangeDaily range• Monthly meanMonthly mean• Annual meanAnnual mean• Annual temperature rangeAnnual temperature range

Mean monthly temperatures Mean monthly temperatures for two locations in Canadafor two locations in Canada

Figure 16.27

Mean monthly temperatures for Mean monthly temperatures for two coastal locationstwo coastal locations

Figure 16.29

Temperature measurement Temperature measurement Human perception of temperature Human perception of temperature

• Anything that influences the rate of heat Anything that influences the rate of heat loss from the body also influences the loss from the body also influences the sensation of temperature sensation of temperature

• Important factors areImportant factors are• Air temperatureAir temperature• Relative humidityRelative humidity• Wind speedWind speed• SunshineSunshine

Controls of temperature Controls of temperature Temperature variationsTemperature variations Receipt of solar radiation is the most Receipt of solar radiation is the most

important controlimportant control Other important controlsOther important controls

• Differential heating of land and water Differential heating of land and water • Land heats more rapidly than water Land heats more rapidly than water • Land gets hotter than waterLand gets hotter than water• Land cools faster than water Land cools faster than water • Land gets cooler than water Land gets cooler than water

Controls of temperature Controls of temperature

Other important controlsOther important controls • AltitudeAltitude• Geographic positionGeographic position• Cloud coverCloud cover• AlbedoAlbedo

World distribution World distribution of temperature of temperature

Temperature mapsTemperature maps • IsothermIsotherm – a line connecting places of – a line connecting places of

equal temperatureequal temperature• Temperatures are adjusted to sea level Temperatures are adjusted to sea level • January and July are used for analysis January and July are used for analysis

because they represent the temperature because they represent the temperature extremes extremes

World distribution World distribution of temperature of temperature

Global temperature patterns Global temperature patterns • Temperature decreases poleward from the Temperature decreases poleward from the

tropics tropics • Isotherms exhibit a latitudinal shift with the Isotherms exhibit a latitudinal shift with the

seasons seasons • Warmest and coldest temperatures occur Warmest and coldest temperatures occur

over land over land

World distribution World distribution of temperature of temperature

Global temperature patterns Global temperature patterns • In the Southern Hemisphere In the Southern Hemisphere

• Isotherms are straighter Isotherms are straighter • Isotherms are more stable Isotherms are more stable

• Isotherms show ocean currents Isotherms show ocean currents • Annual temperature range Annual temperature range

• Small near equator Small near equator • Increases with an increase in latitude Increases with an increase in latitude • Greatest over continental locations Greatest over continental locations

World mean sea-level World mean sea-level temperatures in Januarytemperatures in January

Figure 16.32

World mean sea-level World mean sea-level temperatures in Julytemperatures in July

Figure 16.33